1. Field of the Art
The present invention relates to a phthalocyanine dye that is soluble in water.
2. Description of the Prior Art
Phthalocyanine and its metal complexes (FIG. 1) are organic dyes having a large π conjugate system.
However, those dyes have a planar feature high enough to cause interactions to take place between dye molecules, making it poorly soluble not only in water but in general organic solvents as well.
To solve this problem, many attempts have so far been made, which includes an attempt wherein the hydrogen atoms in benzene rings on the outer side of phthalo-cyanine are substituted by other side-chain groups or an axial ligand is coordinated in a phthalocyanine complex to make solubility in general organic solvents much higher, as reported in Non-Patent Publications 1 to 5 and Patent Publication 1. However, nearly all of them were unsuccessful in improvements in their water solubility.
Specifically, Non-Patent Publication 1 has reported a phthalocyanine dye that forms hydrophilic colloid, but that colloid is far away from being soluble in water.
In Non-Patent Publication 2, the hydrogen atoms in the benzene rings are substituted by hydrophilic functional groups such as sulfonic acid groups (—SO3H) to introduce some improvements in solubility in water, but significant molecular aggregation occurs in an aqueous solution.
In Non-Patent Publications 3, 4 and 5, the hydrogen atoms in the benzene ring are substituted by hydrophilic functional groups such as carboxyl groups (—CO2H) to introduce some improvements in solubility in water, but significant molecular aggregation occurs in an aqueous solution.
In most of the prior arts, the hydrogen atoms in the benzene rings are substituted by hydrophilic functional groups such as sulfonic acid groups (—SO3H) or carboxyl groups (—CO2H) or their analogs to improve solubility in water. However, it has been known that the phthalo-cyanine that is made water soluble in this way causes significant molecular aggregation (that is a phenomenon in which multiple molecules behave as if they were one single molecule) at high concentrations, giving rise to losses of the characteristic features inherent in the phthalocyanine dye (photochemical feature in particular).
In Patent Publication 1, axial ligands X and Y derived from an oxidizing agent are used as the groups capable of being coordinated at the antimony of an antimony/phthalocyanine complex; however, that publication refers only to halogens, organic peroxides, peracids or acid halides, saying nothing about the selection of a specific axial ligand for improving water solubility.